Digital camera systems may include a lens for focusing an image onto an image sensor. Often lenses are composed of several optical elements. Some of the optical elements of the lens may be movable relative to the lens body, which results in optical characteristics of the lens being changed. For example, in varifocal lenses, changing the position of some of the optical elements results in a change in the focal length of the lens as the image is zoomed in or out.
The control of zooming in and out may be accomplished in various ways depending upon the camera system. In security cameras or other video cameras used to remotely survey a location, the camera system, including the zoom level, may be controlled. In addition to the zoom control, camera systems may also include additional positioning motors for adjusting a direction the camera system points in. These positioning motors may include a pan motor and a tilt motor. Typically, cameras with these motors may be referred to as pan, tilt and zoom (PTZ) cameras. When zooming in on a specified location, a user expects the zoom movement to be centered. That is, it is expected that a center point in the zoomed-out image will also be centered in the zoomed-in image. However, the image sensor may not be perfectly aligned with the optical axis of the lens and as such, as the image is zoomed in or out, the image will become un-centered and the user experiences an image shift.
FIG. 1 depicts a scene that may be captured by a camera system. As depicted, a city scene 100 is captured at different magnification levels, as depicted by field of view rectangles 102, 104, 106. As depicted, when the scene is captured at a first magnification level 102, the center of the field of view, represented by circle 108 is centered within the field of view 102. As the image is zoomed-in to a second magnification level 104, the circle 108 is no longer centered. As the image is zoomed in further 106, the error becomes more detectable and may result in the point 108 being completely outside of the field of view 106. The offset between the center of the image when completely zoomed out (i.e. wide end of the lens) and the center of the image when completely zoomed in (i.e. telephoto end of the lens) is called the “bore-sight offset” of the imaging module.
Camera systems may attempt to correct for this error. FIG. 2 depicts an existing adjustment scheme used to correct for bore-sight offset error. As depicted, previous correction techniques 200 zoomed into the image (202) and then subsequently adjusted the positioning of the field of view (204) to correct for the offset error resulting from the zoom movement that was performed. While the final positioning using this technique may center the zoomed-in image correctly, the image will first be zoomed in followed by repositioning. Accordingly, the zooming process may not be fluid and the user experience is not ideal.
It is desirable to have an additional, alternative and/or improved camera system control to correct for bore-sight offset error.